Vokuro and Phalcon 2.0 Problem

it says

Fatal error: Class 'Vokuro\Acl\Acl' not found in /var/www/php/phalcon/vokuro/app/config/services.php on line 146

$loader->registerNamespaces(array(
    'Vokuro\Models' => $config->application->modelsDir,
    'Vokuro\Controllers' => $config->application->controllersDir,
    'Vokuro\Forms' => $config->application->formsDir,
    'Vokuro' => $config->application->libraryDir
));

anyone know why it happened?